1. Field of the Invention
This invention relates to an optical apparatus having a diaphragm device which is arranged to vary the full-open aperture diameter thereof according to zooming.
2. Description of the Related Art
The aperture of a diaphragm device disposed at the interchangeable lens of a single-lens reflex camera is arranged to be always kept in a full-open state to permit light measurement with the aperture fully opened and to be stopped down immediately before a shutter release. The camera system of this kind is provided with a switch for detecting the full-open state of the diaphragm device as in the case of, for example, a camera system disclosed in U.S. Pat. No. 4,841,327. In order to vary the full-open aperture diameter according to a zooming operation on the lens in the camera system of this kind, it has been practiced to use a cam mechanism for interlocking the diaphragm device with a zoom mechanism with the full-open state detecting switch set in a fixed position.
In the conventional camera system described above, the mechanism for mechanically varying the full-open aperture diameter according to zooming is provided in the lens barrel of the camera system. Therefore, the lens barrel has necessitated a complex structural arrangement, which has increased the cost of the camera system.